Is there something particularly difficult in pipetting washed red cells as opposed to, say, pipetting 1.5 ml of saline? If you're trying to achieve equal numbers of cells per aliquot from different samples, accurate volume is not the answer without knowing the number of cells per volume unit.

Is there something particularly difficult in pipetting washed red cells as opposed to, say, pipetting 1.5 ml of saline? If you're trying to achieve equal numbers of cells per aliquot from different samples, accurate volume is not the answer without knowing the number of cells per volume unit.

I think I'm losing some volume because it's viscous. I need an accurate volume because I'm using the red blood cells to dilute a standard out (1.5mL red blood cells to 1.5mL of standard).

In that case, a positive displacement pipette is better than an air displacement pipette. A syringe might also be a better choice (as was suggested) if the accuracy of the graduations on a syringe is high enough (I don't know how accurate a typical syringe's markings are, nor how accurate the measurement-to-measurement reproducibility will be with a syringe).

I use two methods for accurately pipet blood.
With a tip
First pipette the blood very slowly. When taking blood in let the piston come up slowly and wait for 20-30 seconds so you're sure the blood is in.
Then slowly push the piston down and watch very carefully if all the blood from the wall of the tip is coming down, if not you're pushing to fast. It,s a very slow proces it can take minutes.
(With a glass pipet it works the same)

Much faster is using a positive displacement pipette as mentioned before.

Weight is not a solution because the specific weight of blood is not known therfor you can't calculate the volume.

I use two methods for accurately pipet blood.With a tipFirst pipette the blood very slowly. When taking blood in let the piston come up slowly and wait for 20-30 seconds so you're sure the blood is in.Then slowly push the piston down and watch very carefully if all the blood from the wall of the tip is coming down, if not you're pushing to fast. It,s a very slow proces it can take minutes.(With a glass pipet it works the same)

Much faster is using a positive displacement pipette as mentioned before.

Weight is not a solution because the specific weight of blood is not known therfor you can't calculate the volume.

Thanks everyone, I think I'm going to try the positive displacement pipette. It seems like it will be the easiest and quickest solution.

You can use the pipette of 1000 microlitre and pipette out 1000 ml blood for rest 500 ml you can set the 1000 microlitre pipette to 500 and pipette out the rest blood.It will give the accurate blood amount.

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The use of reverse pipetting helps. Just pushed right to the 2nd stop of the pipette and draw the fluid in excess, dispense only to the 1st stop. This will accurately dispense the amount without any retention in the pipette tip.